Not sure this is the right place, my German is not that good! Together with two friends I made a comparison of some coarse synthetic sharpening stones, which can be found here. Comments are more than welcome!
& Thank You for the pointer to that review. It was an interesting read. :-) Having tested quite some synthetic stones in the last month, I'd recommend to have a look on the Naniwa Pro 400, too. For the time being, this is my favourite coarse stone. Regarding the 500JIS glass stone, I'd count the to the medium stones, too. Very handy to get rid of scratches from the real coarse steel eaters.